blit: handle emulated alpha sources as well just in case.

We haven't seen this yet, but it is a potential problem we should fix.

src/vrend_blitter.c

@@ -600,6 +600,9 @@ void vrend_renderer_blit_gl(struct vrend_context *ctx,
 
    glBindTexture(src_res->target, src_res->id);
 
+   if (vrend_format_is_emulated_alpha(info->src.format))
+      glTexParameteri(src_res->target, GL_TEXTURE_SWIZZLE_R, GL_ALPHA);
+
    glTexParameteri(src_res->target, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(src_res->target, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glTexParameteri(src_res->target, GL_TEXTURE_WRAP_R, GL_CLAMP_TO_EDGE);

src/vrend_renderer.c

@@ -5498,7 +5498,8 @@ static void vrend_renderer_blit_int(struct vrend_context *ctx,
    if (info->src.box.depth != info->dst.box.depth)
       use_gl = true;
 
-   if (vrend_format_is_emulated_alpha(info->dst.format))
+   if (vrend_format_is_emulated_alpha(info->dst.format) ||
+       vrend_format_is_emulated_alpha(info->src.format))
       use_gl = true;
 
    if (use_gl) {